The measurement of exposure to ultrasound and its application to estimates of ultrasound 'dose'

Abstract

There has been considerable progress towards the identification of relevant physical quantities and towards developing experimental methods for ultrasound exposure measurement in water. This review considers the range of transducer shapes and pulsing regimes used in medical ultrasonics. Analysis of the variety of fields generated is made possible using an impulse response approach allowing the separation of source shape from source vibration. Finite-amplitude distortion of pulse waveforms has been found to be of considerable significance at the pressures experienced. Measurements using miniature piezoelectric polymer hydrophones present the most accurate method of gaining information about the pressure fields and various intensity values may then be derived which allow comparisons between fields. Problems still exist in definitions of pulse duration and beam area, with consequent uncertainty in quantities that are calculated using these parameters. It seems advisable to use, as a minimum record of a beam characteristic, the pressure waveform recorded using a calibrated hydrophone. It seems unlikely that intensity values alone will be adequate for the description of ultrasonic fields in a way which will be completely suitable for specification of ultrasonic 'tissue dose'.